1. Field of the Invention
This invention relates to an oxidation process for preparing quinone alkides from the corresponding tri-alkyl or phenyl hindered phenols using minor amounts of ferrocyanide or ferricyanide in combination with persulfate in an oxidation-reduction reaction. The quinone alkides are especially suitable for use as polymerization inhibitors for styrene monomer.
2. Description of the Prior Art
It is known that alkaline ferricyanide can be used as an oxidizing agent in combination with other compounds, for example, U.S. Pat. No. 3,660,505, Starnes, issued May 2, 1972, teaches the reduction of quinone methides to the corresponding phenols utilizing an alkyl or aralkyl Grignard reagent and the subsequent oxidation of the phenol with basic ferricyanide to produce a new quinone methide, followed by reacting the compound with a tertiary amine or a trialkylphosphine to produce an alkenyl phenol. The resulting product is described as suitable for use as antioxidants for hydrocarbons and especially for polyolefins such as polypropylene.
Filar et al, Tetrahedron Letters, Preparation and Behavior of Simple Quinone Methides, NO. 25, pp. 9-16 (1960), disclose the oxidation of phenols with silver oxide or lead dioxide to produce the quinone methide analog. The reference is primarily a broad overview of the behavior of simple quinone methides, which discloses the stability and reactivity of said quinone methides.